Ventilation analysis and monitoring

ABSTRACT

A ventilation analysis system comprising an interface module adapted to receive a carbon dioxide (CO 2 ) signal and a breath flow dynamics signal, and control logic adapted to produce a ventilation indicator, based on a mutual analysis of the CO 2  signal and the breath flow dynamics signal. The ventilation indicator may be, for example, an estimated CO 2  waveform, an End-Tidal CO 2  (ETCO 2 ) value, and/or a minute CO 2  value.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 12/999,111 (published as US 2011/0105935), filed Dec. 15, 2010, which is the U.S. National Stage of International Application No. PCT/IL2009/000651, filed Jun. 30, 2009, which claims the benefit of U.S. Provisional Patent Application No. 61/129,474, filed Jun. 30, 2008, the contents of each of which are expressly incorporated herein in their entireties by this reference.

FIELD

Embodiments of the disclosure relate to ventilation analysis and monitoring in patients.

BACKGROUND

Capnography is often defined as the measurement of the level of carbon dioxide (CO₂) in exhaled and/or inhaled breath. Since infrared light was found to be absorbed particularly well by CO₂, capnographs usually measure infrared absorption in the breath gasses, which indicates the level of CO₂ in these gasses. Other measurement technologies exist as well.

The information obtained from a capnographic measurement is sometimes presented as a series of waveforms, representing the partial pressure of CO₂ in the patient's exhaled breath as a function of time.

Clinicians commonly use capnography in order to assess a patient's ventilatory status. Respiratory arrest and shunt may be speedily diagnosed, and a whole range of other respiratory problems and conditions may be determined by the capnographic measurement. Capnography is considered to be a prerequisite for safe intubation and general anesthesia, as well as for correct ventilation management.

Breath flow dynamics is another ventilation-related factor that is sometimes being measured. Whereas capnography is usually indicative of physiological aspects of ventilation, breath flow dynamics measurement is often indicative of the mechanics of respiration—the inhalation and exhalation activity of patient's lungs.

SUMMARY

There is provided, according to embodiment, a ventilation analysis system comprising: an interface module adapted to receive a carbon dioxide (CO₂) signal and a breath flow dynamics signal; and control logic adapted to produce a ventilation indicator, based on a mutual analysis of said CO₂ signal and said breath flow dynamics signal.

There is further provided, according to an embodiment, a method for ventilation analysis, the method comprising: receiving a CO₂ signal and a breath flow dynamics signal; and mutually analyzing the CO₂ signal and the breath flow dynamics signal, to produce a ventilation indicator.

In some embodiments, said ventilation indicator comprises an estimated CO₂ waveform, an End-Tidal CO₂ (EtCO₂) value and/or a minute CO₂ value.

In some embodiments, the system further comprises a CO₂ sensor adapted to produce said CO₂ signal.

In some embodiments, said CO₂ sensor comprises a wireless CO₂ sensor.

In some embodiments, said CO₂ sensor comprises a CO₂ sensor having a response time of 100 milliseconds (ms) or more, 500 ms or more and/or 900 ms or more.

In some embodiments, the system further comprises a breath flow dynamics sensor adapted to produce said breath flow dynamics signal.

In some embodiments, said breath flow dynamics sensor comprises a wireless breath flow dynamics sensor.

In some embodiments, said breath flow dynamics sensor comprises a flow sensor, an acoustic sensor, a thermal sensor, a chest movement detector, a computer-aided video analyzer and/or a Doppler radar.

In some embodiments, said interface module is further adapted to receive a Saturation of Peripheral Oxygen (SpO₂) signal.

In some embodiments, the system further comprises an SpO₂ sensor adapted to produce said SpO₂ signal.

In some embodiments, the receiving of the CO₂ signal comprises wirelessly receiving the CO₂ signal.

In some embodiments, the CO₂ signal comprises discrete Partial Pressure CO₂ (PCO₂) readings taken every 100 ms or more, every 500 ms or more and/or every 900 ms or more.

In some embodiments, the receiving of the breath flow dynamics signal comprises wirelessly receiving the breath flow dynamics signal.

In some embodiments, the breath flow dynamics signal comprises a flow measurement, an acoustic measurement, a thermal measurement, a chest movement measurement, a computer-aided video analysis and/or a Doppler radar signal.

In some embodiments, the method further comprises receiving an SpO₂ signal.

In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the figures and by study of the following detailed description.

BRIEF DESCRIPTION OF THE FIGURES

Exemplary embodiments are illustrated in referenced figures. Dimensions of components and features shown in the figures are generally chosen for convenience and clarity of presentation and are not necessarily shown to scale. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive. The figures are listed below.

FIG. 1 schematically shows a block diagram of a ventilation analysis system;

FIG. 2 schematically shows a graph of CO₂ and breath flow dynamics signals;

FIG. 3 schematically shows an estimated CO₂ waveform;

FIG. 4 schematically shows an adult normal capnogram; and

FIGS. 5A-C schematically show capnogram patterns.

DETAILED DESCRIPTION

An aspect of some embodiments of the disclosure relates to a ventilation analysis and/or monitoring system. The system may be adapted to interface with one or more sensors to receive a carbon dioxide (CO₂) signal and a breath flow dynamics (hereinafter “BFD”) signal, both pertaining to a patient. The received signals may be mutually analyzed, to produce a ventilation indicator that may assist a clinician in assessing the patient's ventilatory condition.

Advantageously, the CO₂ signal may be received from a CO₂ sensor adapted to operate with a relatively slow response time. In some embodiments, this may enable the use of a relatively small, power efficient and/or simple sensor, compared to conventional CO₂ sensors commonly used today in conjunction with capnographs. Various CO₂ sensors are being constantly introduced to the market, where one of the major improvements these sensors offer is faster and faster response times. Response time is often defined as the duration between two consecutive samples taken by the CO₂ sensor. For example, a sensor having a response time of 50 milliseconds (ms), is able to measure (or “read”) momentary breath CO₂ concentration once every 50 ms, which amounts to 20 measurements per second. A faster response time means a shorter response time and therefore more measurements per second.

Generally, faster response times enable the creation of a CO₂ waveform (or “graph”) having a greater resolution. A CO₂ waveform is a graphic representation of the breath CO₂ concentration over time, which is sometimes displayed by capnographs. If more CO₂ readings are available per a unit of time, the resolution of the waveform increases, and so does its accuracy and the amount of meaningful information it may relay to a clinician. Therefore, newly-introduced capnographs often aim to offer faster response times than before. However, there is often a tradeoff between response time and factors like manufacturing complexity, power consumption, physical size and weight, cost and/or the like.

Therefore, in an embodiment, the ventilation analysis and/or monitoring system is advantageously adapted to provide a clinically-meaningful ventilation indication while utilizing a CO₂ sensor having a relatively slow response time, such as a response time in the range of 100-300 ms, 300-500 ms, 500-700 ms, 700-900 ms, 900-1100 ms or above 1100 ms. This may enable the use of a relatively simple, small, low power, lightweight and/or otherwise more cost-effective CO₂ sensor. In other embodiments, a CO₂ sensor may nonetheless have a relatively fast response time, such as a response time of below 100 ms.

The ventilation analysis and/or monitoring system may provide the ventilation indication by pairing a signal received from the CO₂ sensor with a signal received from a BFD sensor. BFD, which is often indicative of the mechanics of respiration—the inhalation and exhalation activity of patient's lungs, may be measured using various methods known in the art. For example, a flow sensor is sometimes positioned about the patient's nostrils or mouth, directly measuring the dynamics of inward and/or outward gas flow. If the patient is intubated and given artificial respiration, a measurement of the BFD may be provided by the respirator.

Measurement of BFD may also be performed essentially indirectly, such as using an acoustic sensor sensitive to sound emitted during respiration, a thermal sensor sensitive to temperature changes during respiration, a chest movement detector attached to the patient's body, a microwave Doppler radar system adapted to produce a signal indicative of chest movement and/or a computer-aided video analyzer adapted to visually recognize chest movement.

BFD may provide information such as a numerical respiration rate value and/or a visual indication of exhalation/inhalation cycles over a time axis. A respiration rate is often defined as the number of exhalation/inhalation cycles per minute, and is commonly considered a clinical parameter of great importance. A visual indication may include a graph showing the exhalation/inhalation spread over a time axis.

Reference is now made to FIG. 1, which shows a block diagram 100 of a ventilation analysis and/or monitoring system (hereinafter “system”) 102, in accordance with an embodiment. System 102 may be essentially what is often referred to as a capnograph, or be incorporated within a capnograph.

System 102 may include an interface module 104 adapted to interface with a CO₂ sensor 110 and with a BFD sensor 112, which measure breath CO₂ concentration and BFD, respectively, of a patient. The interface with each of CO₂ sensor 110 and BFD sensor 112 may be wired or wireless. Optionally, CO₂ sensor 110 and BFD sensor 112 are enclosed within a single physical unit, which may be referred to as a multi-purpose sensor adapted to sense both CO₂ and BFD.

Interface module 104 may further be adapted to interface with an SpO₂ sensor (not shown), to receive an SpO₂ signal.

Interface module 104 may periodically receive a CO₂ signal from CO₂ sensor 110 and a BFD signal from BFD sensor 112, and make these signals available to a control logic 106. Control logic 106 may mutually analyze the CO₂ and BFD signals, and output (or “produce”) one or more ventilation indicator(s) 114 based on both signals.

An example of a ventilation indicator is a CO₂ waveform 116. As mentioned, conventional capnographs may require a fast-response CO₂ sensor in order to produce a CO₂ waveform of a sufficiently high resolution. Nonetheless, CO₂ waveform 116 may be produced based on the BFD signal and on the CO₂ signal which may be of a slow-response CO₂ sensor. The creation of CO₂ waveform 116 is further discussed below.

In addition to CO₂ waveform 116, other ventilation indicator(s) 118 may be created from the mutual analysis of the BFD and CO₂ signals. For example, a ventilation indicator may be end-tidal CO₂ (EtCO₂), minute EtCO₂ and/or the like. These ventilation indicators are further discussed below.

System 102 may be further adapted to relay to a clinician, visually and/or sonically, SpO₂ values derived from the received SpO₂ signal.

System 102 may be embodied in a computerized device having input, output and processing abilities to carry out operations of interface module 104 and control logic 106. For example, system 102 may be an essentially stationary computerized device positioned next to a patient's hospital bed or at a central location in the hospital (if remote monitoring of a patient is desired). As another example, system 102 may be an essentially mobile computerized device adapted to be carried by an emergency clinician, in an ambulance and/or the like. A patient whose ventilatory condition is desired to be monitored may be connected to CO₂ sensor 110 and BFD sensor 112, which transmit their readings to system 102 for analysis. The output of system 102, namely—ventilation indicator 114, may be relayed to the clinician by way of visual display on a monitor, sonic indication and/or the like.

In an embodiment, system 102, or another system (not shown) adapted to receive CO₂ and BFD signals, may provide a ventilation indicator or different ventilatory status having enhanced reliability. The enhanced reliability may be achieved since CO₂ and BFD are two measures of essentially the same system—the body ventilatory system. Each of these measures offers a different perspective of essentially the same bodily system, and therefore these measures complement each other. Monitoring both measures may allow the filtering out of issues such as false or poor readings arriving from one of the two sensors due to a defect or an error, and/or cases in which the patient is talking, eating, coughing and the like and therefore temporarily exhibiting irregular CO₂ and/or BFD signals.

Reference is now made to FIG. 2, which shows a graph 200 of exemplary signals that may be transmitted from CO₂ sensor 110 and BFD sensor 112 to interface module 104 (FIG. 1).

A BFD signal 202 may indicate a respiratory state of the patient, such as whether the patient is currently exhaling or inhaling, and/or the intensity of the exhaling/inhaling at any particular moment. For example, a concave shape 202 a of BFD signal 202 may be indicative of inhalation, whereas a convex shape 202 b of the BFD signal may be indicative of exhalation.

A partial pressure CO₂ (PCO₂) signal, shown as discrete PCO₂ readings 204, may indicate one or more physiological aspects of ventilation. Horizontal distances between PCO₂ readings 204 may be dictated by a response time of the sensor that performed the reading. Since PCO₂ during inhalation is zero, zero readings 204 a may be present during the inhalation. Other readings 204 b, usually higher than zero, may be present during exhalation.

A PCO₂ average signal 206 may show an average of PCO₂ over time. A CO₂ sensor may average PCO₂ readings it performs, producing PCO₂ average signal 206, by using a capacitor and/or similar electronic means. PCO₂ average signal 206 is shown in the figure as a straight line 206 a, for illustrative purposes only.

A CO₂ sensor may transmit either PCO₂ readings 204, PCO₂ average signal 206, or both.

Reference is now made to FIG. 3, which shows an exemplary estimated CO₂ waveform 300, which is optionally the ventilation indicator produced by the ventilation analysis and/or monitoring system. The exemplary estimated CO₂ waveform 300, like common CO₂ waveforms, may contain trapezoid-like shapes, such as trapezoid 302. An upsurge curve 302 a of trapezoid 302 indicates a beginning of an exhalation, a gradually rising curve 302 b indicates a central part of the exhalation, and a drop curve 302 c indicates an ending of the exhalation. A zero-value curve 302 d indicates an inhalation.

Those of skill in the art will recognize that the shape of the trapezoids usually changes according to the medical condition of the patient, and that estimated CO₂ waveform 300 is meant for illustrative purposes only.

In an embodiment, estimated CO₂ waveform 300 may be constructed by way of the mutual analysis of the CO₂ and BFD signals, despite the slow response time of the CO₂ sensor. For example, if PCO₂ average signal 206 (FIG. 1) is provided by the CO₂ sensor, it may be possible to calculate what was the PCO₂ during exhalation. For instance, if the average PCO₂ is 20, and it is known that: (a) during inhalation the PCO₂ is zero; and (b) the duty cycle of the exhalation and inhalation, as apparent from the BFD signal, is 50%—then the average PCO₂ during exhalation is 40. A trapezoid, such as trapezoid 302, may then be constructed according to a mathematical constraint that the trapezoid's average value must be 40. Another mathematical factor that may be helpful in the construction of the trapezoid is that the product of the average PCO₂ during exhalation (in our example, 40) and the duration of the exhalation (which may be inferred from the BFD signal) is equal to an area that should be delimited between the constructed trapezoid and the time axis.

The BFD signal may provide information pertaining to starting and ending points of the inhalations and exhalations, so that any constructed trapezoids, such as trapezoid 302, may be synchronized with breath cycles.

If discrete PCO₂ readings 204 (FIG. 2) are provided by the CO₂ sensor, a general shape of a trapezoid may be available through other readings 204 b (FIG. 2). One or more methods may be employed in order to fill in the gaps between other readings 204 b and enhance the resolution of the trapezoid. For example, other readings 204 b (FIG. 2) may be averaged and then treated similarly to the average PCO₂ described above. As another example, other readings 204 b (FIG. 2) may be synchronized with breath cycles provided by the BFD signal, so that a location and an estimated shape of parts like upsurge curve 302 a, gradually rising curve 302 b, drop curve 302 c and zero-value curve 302 d may be determined.

In an embodiment, the ventilation indicator is an EtCO₂ value. EtCO₂ is often defined as the partial pressure of CO₂ at a point in time when CO₂ values stop increasing and on the verge of dropping. An exemplary EtCO₂ point 304 is shown in FIG. 3.

The creation of EtCO₂ indication may be enabled, despite the slow response time of the CO₂ sensor, via mathematical calculation. The EtCO₂ may be calculated similar to the way the CO₂ waveform may be created, as discussed above. If an estimated shape of a trapezoid is calculated, EtCO₂ for each trapezoid may also be calculated.

In an embodiment, the ventilation indicator is a minute CO₂ value. Minute CO₂ is commonly referred to as the total production of CO₂ per minute. By correlating the BFD signal with the PCO₂ average or discrete readings, minute CO₂ may be calculated. More specifically, when using a PCO₂ average signal, inhalation and exhalation cycles may be used to determine the PCO₂ average during exhalation alone. This exhalation PCO₂ may then be multiplied by a respiration rate (also obtainable from the BFD signal) to output minute CO₂.

Reference is now made to FIG. 4, which shows an adult normal capnogram 400 as known in the art. Adult normal capnogram 400 in spontaneously breathing subjects may be characterized by four distinct phases:

-   -   1. Dead space ventilation: Shown between points 402 and 404 in         the figure, this is the earliest phase of exhalation.         Physiologally, this phase corresponds to initial exhalation from         upper airway (mainstem bronchi, trachea, posterior pharynx,         mouth and nose).     -   2. Ascending phase: Shown between points 404 and 406 is a rapid         rise in CO₂ concentration, which physiologically crresponds to         alveolar gas reaching the upper airways.     -   3. Alveolar plateau: Shown between points 406 and 408, this is         the stage where CO₂ reaches a generally steady state, sometimes         having a mild ascending slope. Physiologally, this phase         corresponds to a uniform CO₂ level attained in the entire breath         stream.     -   4. Inspiratory limb: Shown between points 408 and 410 is a rapid         decrease in CO2 concentration back to zero, marking the         beginning of an inhalation.

Point 408, which is the intersection of the alveolar plateau and the inspiratory limb, is often referred to as the End-Tidal CO₂ (EtCO₂).

An angle α, which designates the angle between the ascending phase curve and the X axis, is referred to as a “takeoff angle”. An angle β, which designates the angle between the alveolar plateau and the X axis, is referred to as an “elevation angle”.

An amplitude of capnogram 400 is dependent on EtCO₂ concentration. A width of capnogram 400 is dependent on expiratory time. The shape of capnogram 400 is generally rectangular, formed by almost perpendicular ascending phase (indicating absence of lower airway obstruction) and inspiratory limb (no upper airway obstruction).

Reference is now made to FIGS. 5A, 5B and 5C, which show exemplary capnogram patterns. FIG. 5A shows a capnogram 500 demonstrating elevated EtCO₂ with a good alveolar plateau. A corresponding graph 502 shows a 30-minute trend exhibiting a constant but elevated EtCO₂. Possible causes may be: (a) inadequate minute ventilation or hypoventilation; (b) respiratory depressant drugs; (c) hyperthermia, pain and/or shivering.

FIG. 5B shows a capnogram 504 demonstrating gradually increasing EtCO₂. A corresponding graph 506 shows a 30-minute trend exhibiting this gradual increase. Possible causes may be: (a) hypoventilation; (b) rising body temperature and/or malignant hyperthermia; (c) increased metabolism; (d) partial airway obstruction; (e) absorption of CO₂ from exogenous source.

FIG. 5C shows a capnogram 508 demonstrating an alveolar cleft. A corresponding graph 510 shows a 30-minute trend exhibiting constant EtCO₂ levels. Possible causes may be inadequate neuromuscular blockade and/or emergence from blockade.

While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced be interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.

In the description and claims of the application, each of the words “comprise” “include” and “have”, and forms thereof, are not necessarily limited to members in a list with which the words may be associated. 

What is claimed is:
 1. A low power, light weight medical device comprising: a user interface comprising a CO₂ sensor configured to measure a CO₂ concentration in a subject's breath, said CO₂ sensor having a response time below 100 ms; a control logic configured to produce a ventilation indicator based on CO₂ concentration measurements obtained from said CO₂ sensor; and a display configured to display said ventilation indicator and to provide a numerical respiration rate value and/or a visual indication of exhalation and/or inhalation cycles over a time axis.
 2. The medical device of claim 1, wherein said user interface further comprises a breath flow dynamics (BFD) sensor.
 3. The medical device of claim 2, wherein said ventilation indicator is further produced based on BFD measurements obtained from said BFD sensor.
 4. The medical device of claim 2, and wherein said BFD sensor is a flow sensor.
 5. The medical device of claim 1, further configured to provide a visual and/or sonic indication related to said ventilation indicator.
 6. The medical device of claim 1, wherein said ventilation indicator comprises an estimated CO₂ waveform, an End-Tidal CO₂ (EtCO₂) value and/or a minute CO₂ value.
 7. The medical device of claim 6, wherein said ventilation indicator comprises an estimated CO₂ waveform and an End-Tidal CO₂ (EtCO₂) value.
 8. The medical device of claim 1, wherein said CO₂ sensor has a response time below 50 ms. 